Reconstruction of the anterior and posterior cruciate ligaments is an increasingly popular orthopedic operation resulting from an increasingly active lifestyle of the populace. Strenuous physical activities involved in this type of lifestyle may cause injuries which result in instability of the knee which must be reconstructed, generally in the form of the aforementioned ligament reconstruction procedures. In addition to correcting knee instability, ligament reconstruction may also provide a secondary beneficial effect of possibly reducing the incidence of secondary arthritis or secondary meniscal tears.
Of the general ligament reconstruction procedures, the most popular is that of "bone-patella tendon-bone". In this procedure or technique, a central 9 or 10 mm portion of the patella tendon is harvested with its attachment onto the patella and tibial tubercle, with a plug of bone which is usually about 25 mm in length and about 9 or 10 mm in width. The graft itself may be cylindrical or trapezoidal in shape depending on surgeon preference.
In the procedure, a hole is drilled into the intercondylar notch of the femur on the lateral side just above the "over-the-top" position. This follows formation of a hole in the tibia which extends from the anteromedial surface into the center of the tibial articular surface, about 7 mm from the posterior cruciate ligament. The bone-patella tendon-bone construct is threaded up through the tibia into the knee and then pulled into the femoral hole. In order for the patient to immediately begin a range of motion program, it is desirable, if not necessary, to provide immediate and secure fixation for both ends of the grafts, whereby the patient can move the knee and begin early bearing exercises.
Several fixation devices have been developed and are available in order to provide the requisite secure fixation. The most popular of such devices is the "interference" screw, with a biologically inert screw being inserted in the femoral hole at the interface between the bone plug of the graft and the host femoral bone. The threads of the screw bite into the graft and the host bone and hold the graft firmly against the bone. The screw can be inserted at the femoral side and the tibial side, but the tibial side is more problematic, particularly if the graft is too short or too long. Accordingly, on the tibial side, the graft is often "posted" via sutures attached to the graft over a cancellous screw and washer, inserted into the tibial bone at some distance away from the previously drilled tibial hole.
There are however, problems and shortcomings which are associated with the "interference" screw fixation procedure. Foremost of these problems is an inherent one related to the operation of the fixation screw. The graft or the posterior cruciate ligament may be damaged by the very insertion of the interference screw, generally as a result of the threads which must bite into the bone for operable fixation. Furthermore, the screw head, because of its close juxtaposition, may impinge on the graft, thereby contributing to further stretching and/or rupture thereof. Size of the screw is also of critical importance since an oversized screw can crush the graft and an undersized screw will provide inadequate fixation. Use of a screw of an incorrect size often will also disrupt the integrity of the fixation site or graft, thereby necessitating use of a different fixation means. This is particularly true on the femoral side and an adjunct technique then becomes necessary. On the tibial side, problems arise with posting such as loosening of the graft and difficulty in tying sutures over the post with adequate tension in order to keep the graft appropriately taut. Often the graft will loosen or the sutures will loosen or the sutures may be cut or severed by the screw threads. If a change is needed, the screw must be removed and another must be reinserted, which can further compromise the graft.